SNAP-tag technology: a powerful tool for site specific conjugation of therapeutic and imaging agents.

In the past two decades, immense advances have been achieved in the engineering, production and purifying of recombinant proteins. These proteins are being widely utilized in many fields of biology, biotechnology and medicine, including diagnostic and therapeutic applications. These applications often require the modification or conjugation of these proteins with other molecules. Researchers are spending many efforts to develop and improve the methods of protein modifications. A main challenge they face is derivatizing proteins without affecting their structure and biological function. The conjugation methods available today include random and specific chemical modifications on endogenous amino acids or carbohydrate of the protein of interest. Other methods utilize self-labeling tags as fusion partners to the original protein enabling site-specific conjugation. SNAP-tag is one of the most promising self-labeling tags, which reacts specifically, rapidly and covalently with benzylguanine (BG) derivatives. SNAP-tag fusion proteins have been successfully used for imaging living cells. Recently, several studies have utilized the SNAP technology for generating antibody-based diagnostic and therapeutic tools. We here review these approaches and their possible impact on improving cancer targeting.